Ruh Roh...Amp is blowing fuses

Discussion in 'Amp Central Station' started by chet again, Jul 14, 2020.

  1. chet again

    chet again Tele-Afflicted

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    I said that I had put in an NOS preamp tube the other day. I started playing it before that and noticed the reverb wasn't working. I switched 12AT7 tubes and played it again to see if the reverb came back. It did and after a couple of minutes the fuse blew.
    I got a new fuse and took out the NOS preamp tubes and played it again today. The fuse blew again.

    I notice that a Fender preamp tube I'm using really glows brighter than all the others. Could that be a sign that it's a bad tube?

    The amp is my vintage 1965 Super Reverb. It really sounds nice before it blows fuses. LOL!
     
  2. Javier668

    Javier668 Tele-Meister

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    Open it and take a look.
     
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  3. Milspec

    Milspec Poster Extraordinaire Silver Supporter

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    Start out with no tubes and turn it on....no blow, turn off and insert one tube at a time and repeat until you find the offending tube.

    Once you do find it, order some NOS JAN-Phillips 12AT7 tubes and use it for the reverb tube. Those old military tubes can take a beating.
     
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  4. chet again

    chet again Tele-Afflicted

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    So you think it's probably the reverb tube?
     
  5. Dacious

    Dacious Poster Extraordinaire

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    The tube that's glowing brighter - leave that out and try it.
     
  6. Wally

    Wally Telefied Ad Free Member

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    Vintage amp....has it been properly maintained? Anytime a fuse repeatedly blows, imho it is tech time.
     
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  7. ce24

    ce24 Poster Extraordinaire

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    Rectifier tube possibly. My friends DRRI was doing that and that fixed it,..... It was less than a year old.
     
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  8. Wally

    Wally Telefied Ad Free Member

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    pull all tubes. Install a fresh fuse. Fire it up. If the fuse holds, install the rectifier and being the amp back online. If the fuse holds, install the power tubes.....do this on down the line until the fuse blows. At that point you have found the area of concern....it could be a tube or any other component in that area.

    if the amp has original electrolytics, I do not question anything. I recap the amp, do good general service, and then see what is there.
     
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  9. Dan_Pomykalski

    Dan_Pomykalski TDPRI Member

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    I believe I read somewhere that fuses blowing are normally because of something in the power section. I can't remember for sure though
    I believe fuses blowing are usually a result of something wrong with the power section, so I'd also suggest starting with the rectifier.
     
  10. chet again

    chet again Tele-Afflicted

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    I'm leaving out the tube in V1 and just testing tubes in the 'Vibrato' channel. I don't have enough known good tubes to check out both channels at the same time.

    I took out all preamp tubes and replaced them with 12AX7s that I think are good. I'm just testing one of the 12AT7s now. It's one of the newer Electro-Harmonics tubes. I put a 12AX7A in the Phase Inverter spot. I don't have a third 12AT7 tube.

    I'm taking for granted that the rectifier and power tubes are good. A couple of NOS RCA 6L6GCs and a newer JJ rectifier tube.

    It powered up OK and I played it for a few minutes- watching the tubes from the back. I have good reverb.

    I'll turn it off, let it cool down and turn the amp around and give it a good workout the keep testing these tubes in a little while.
     
  11. chet again

    chet again Tele-Afflicted

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    Well, I think I've narrowed it down.

    You guys may be right and I'm going to replace the rectifier next. I had it running for awhile then turned it off and turned the amp around. I warmed up the tubes and hit the standby switch and all hell broke loose!

    Down to the rectifier, power tubes and one 12AT7 tube.
     
  12. chet again

    chet again Tele-Afflicted

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    Maybe I should start with the power tubes cause it was OK with just the rectifier tube running in it.
     
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  13. Wally

    Wally Telefied Ad Free Member

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    Standby switches??? We don’t need no stink8n’ standby switches!

    there are certain amps that play havoc with modern rectifiers...some of the Vox AC30s for instance.i see no reason to use a standby with most amps. Now, I don’t like to count the 13 relay switches in a Bogner Ecstasy when shutting one of those off without putting the amp on standby. But....standby is not needed for warming tubes because cathode stripping does NOT occur at the low voltages that are in these guitar amps. It takes around 10K volts to strip a cathode.
     
  14. chet again

    chet again Tele-Afflicted

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    Wait...I forgot that this particular Super Reverb does not seem to like it when I take the V1 tube out. I remember I'd tried that before and it didn't like it. I was reading KNOS Tubes tube recommendations about it but forgot what happened when I tried it.

    So I put it back in and will try it again.
     
  15. chet again

    chet again Tele-Afflicted

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    C'mon up to Iowa and troubleshoot this for me. I'm not proud. :D

    There's a nice motel you can stay at right by I-29.
     
  16. chet again

    chet again Tele-Afflicted

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    So I put the V1 preamp tubes back in with an NOS 12AX7A I have. I also have replaced the NOS RCA power tubes with the Fender 6L6GCs. It let it warm up for a few minutes then turned it on and played it for about 15 or 20 minutes.

    The tremelo didn't work so I probably can't use a 12AX7A in there with this amp but the amp held up.
     
  17. chet again

    chet again Tele-Afflicted

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    So it looks like it may be the NOS RCA power tubes that gave up the ghost.

    I need to get an extra 12AT7 also.
     
  18. Wally

    Wally Telefied Ad Free Member

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    Chet, it just isn’t traveling time!! Of course, if I don’t get out of Texas soon, I may not be able to leave.
    Already I cannot go west from here without incurring a two week quarantine in New Mexico!!, eeeehaw....
    now...refresh my memory.....has this Super Reverb been recapped and serviced???.
     
  19. chet again

    chet again Tele-Afflicted

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    Nien.
     
  20. Wally

    Wally Telefied Ad Free Member

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